1. Technical Field
Embodiments of the present invention relate to a semiconductor memory apparatus, and more particularly, to a circuit and method of outputting temperature data of a semiconductor memory apparatus.
2. Related Art
As shown in FIG. 1, a circuit for outputting temperature data of a semiconductor memory apparatus according to the related art includes a temperature detecting circuit (Band Gap Reference Circuit) 100 and an A/D converter 200.
The temperature detecting circuit 100 may use a band gap reference circuit, and has a structure which includes a temperature sensor 110, a voltage adjusting unit 120, and a fuse set 130.
The temperature sensor 110 outputs a temperature voltage VTEMP that is inversely proportional to an internal temperature of a semiconductor memory apparatus by using temperature characteristics of a bipolar junction transistor (BJT), and a first reference voltage VREF that is constant without depending on a change in temperature.
The voltage adjusting unit 120 distributes the first reference voltage VREF by using a plurality of resistors, and outputs second reference voltages VULIMIT and VLLIMIT that determine an upper limit and a lower limit of the temperature voltage VTEMP. At this time, the plurality of resistors include variable resistors, and resistance values of the variable resistors vary according to a fuse code (FS_CODE) value.
The fuse set 130 includes a plurality of fuses, and outputs the fuse code FS_CODE to the voltage adjusting unit 120 according to cutting states of the fuses.
The A/D converter 200 converts the temperature voltage VTEMP into a temperature code TEMP_CODE of a digital format and outputs it. As shown in FIG. 2, the A/D converter 200 includes a comparator 210, a filter 220, a counter 230, an oscillator 240, a multiplexer 250, a decoder 260, and an A/D converter 270. The comparator 210 compares the temperature voltage VTEMP and an analog voltage DACOUT output by the D/A converter 270 and outputs compared result signals INC and DEC. When values of the comparison result signals INC and DEC extremely fluctuate (that is, the comparison result signals INC and DEC include high frequency components), due to an external noise, the filter 220 does not allow the comparison result signals INC and DEC to be output. In contrast, when the values of the comparison result signals INC and DEC rarely fluctuate (that is, the comparison result signals INC and DEC include only low frequency components), the filter 220 outputs counting signals UP and DN for performing an up counting operation and a down counting operation of the counter 230. The counter 230 increases or decreases a value of an initial temperature code TEMP_CODE (for example, 100000) according to the counting signals UP and DN and outputs it. The oscillator 240 generates a clock signal CLK having a predetermined cycle and supplies the clock signal CLK to the filter 220 and the counter 230 through a delay element DLY. The multiplexer 250 outputs a test code signal TEST_CODE or the temperature code TEMP_CODE according to a test mode signal TM. The decoder 260 outputs a decoding signal SW<0:N> that is obtained by decoding the output of the multiplexer 250. The D/A converter 270 converts the decoding signal SW<0:N> into the analog voltage DACOUT in a range of voltage levels of the second reference voltages VULIMIT and VLLIMIT and outputs it.
The operation of the circuit for outputting temperature data of the semiconductor memory apparatus according to the related art that has the above-described structure will now be described.
The temperature detecting circuit 100 operates to perform temperature detection, and outputs the temperature voltage VTEMP and the second reference voltages VULIMIT and VLLIMIT.
The A/D converter 200 performs a tracking operation for searching the temperature code TEMP_CODE that corresponds to the temperature voltage VTEMP by using the temperature voltage VTEMP and the second reference voltage VULIMIT and VLLIMIT.
If a voltage level of the analog voltage DACOUT of the D/A converter 270 that has converted the output of the counter 230 into the analog voltage becomes equal to a voltage level of the temperature voltage VTEMP, the tracking operation is completed. Therefore, the A/D converter 200 outputs a final temperature code TEMP_CODE. The final temperature code TEMP_CODE is stored in a separate register (not shown), and is used in a structure where the final temperature code TEMP_CODE is needed, among inner or outer structures of the semiconductor memory apparatus.
It is possible to perform a test mode to determine whether the circuit for outputting temperature data of the semiconductor memory apparatus according to the related art accurately operates.
After the internal temperature of the semiconductor memory apparatus is adjusted to a specified temperature that corresponds to the test code signal TEST_CODE, the test mode signal TM is enabled.
If the test mode signal TM is enabled, the multiplexer 250 selects the temperature code TEMP_CODE instead of the output of the counter 230 and outputs it to the decoder 260. The output of the decoder 260 is converted into the analog voltage DACOUT by the D/A converter 270 and is then input to the comparator 210.
If the temperature code TEMP_CODE that is output through the filter 220 and the counter 230 is not same as the test code signal TEST_CODE, an error exists during the output of the circuit for outputting temperature data.
The reason why the error occurs during the output of the circuit for outputting temperature data is due to an offset that exists in the second reference voltages VULIMIT and VLLIMIT which determines an output range of the D/A converter 270. That is, a voltage level of at least one of the second reference voltages VULIMIT and VLLIMIT is larger or smaller than a required voltage level.
Accordingly, the fuse that is included in the fuse set 130 of the temperature detecting circuit 100 is selectively cut so as to change the fuse code FS_CODE, and accordingly, the temperature code TEMP_CODE is monitored by changing the voltage levels of the second reference voltages VULIMIT and VLLIMIT. That is, by repeating this process, it is possible to reduce the error that occurs in the circuit for outputting temperature data.
However, the circuit for outputting temperature data of the semiconductor memory apparatus according to the related art has the following problems.
First, since it is not possible to know a fuse code value that enables the output of the desired second reference voltages VULIMIT and VLLIMIT, the fuse code value is changed stepwise so as to approximate the desired reference voltages, which does not accurately correct the error in the circuit for outputting temperature data.
Second, since fuse cutting and monitoring of the output value need to be repeatedly performed so as to allow the desired second reference voltages VULIMIT and VLLIMIT to be output, a correction process is inconvenient and a process time is increased.
Third, because of a characteristic of an analog method that adjusts the second reference voltages VULIMIT and VLLIMIT through the fuse cutting, even if the correction process is completed, the difference between the amounts of unit voltages increased (resolution) in the reference voltages, and an error in the circuit for outputting temperature data occurs due to a change in a specified temperature for performing a test may still exist. Accordingly, even though the above-described correction process is repeated, it is possible to remove the error in the circuit securely for outputting temperature data.